1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to an image forming apparatus having plural developing devices to supply a developer to an image carrier.
2. Description of the Related Art
An image forming apparatus refers to an apparatus that prints an image on a printing medium according to an input image signal. An image forming apparatus is classified as a printer, a copying machine, a fax machine, a multi-function printer which has multiple functions of printing, scanning, copying and faxing, and the like.
As one type of the image forming apparatus, an electrophotographic type image forming apparatus is operated such that light is scanned to a photosensitive body charged to a predetermined electric potential to form an electrostatic latent image on a surface of the photosensitive body and a developer is supplied to the electrostatic latent image to form a visible developer image. The developer image formed on the photosensitive body is directly transferred onto a printing medium, or is transferred onto a printing medium via an intermediate transfer body. The image transferred onto the printing medium is fused to the printing medium through a fusing process.
In the printing operation, the developer image on the photosensitive body or the intermediate transfer body is not totally transferred onto the intermediate transfer body or the printing medium. A portion of the developer remains on the photosensitive body or the intermediate transfer body. Such residual waste developer is removed by a cleaning device, and is stored in a waste developer storage container.
Generally, a cleaning device includes a cleaning blade which is contacted with a surface of an image carrier such as the photosensitive body or the intermediate transfer body with a predetermined pressure. One end portion of the cleaning blade makes friction with the surface of the image carrier, so as to rake out the residual developer on the surface of the image carrier.
If an appropriate amount of developer remains on the surface of the image carrier, a problem does not exist. However, if an inappropriate amount of developer exists on the surface of the image carrier, for example, when the image forming apparatus is warmed up, or if only an inappropriately small amount of developer remains on the surface of the image carrier because a printing medium having a good transfer efficiency is used, a high frictional force is exerted between the cleaning blade and the image carrier, which may create a problem such that the cleaning blade is turned over.
Even if the cleaning blade does not become turned over, an excessive high frictional force between the image carrier and the cleaning blade may cause damage to the image carrier or the cleaning blade or may generate friction noise.
In order to solve the above problems, a method for reducing friction between the image carrier and the cleaning blade is used, which is as follows: an image for lubrication is formed on the image carrier at a predetermined point of time, for example, when the image forming apparatus is warmed up, or at an interval from the printing of one page to the printing of a next page in a successive printing operation.
However, when the above conventional method is applied to a color image forming apparatus having plural developing devices, the following problems may occur.
Generally, a color image forming apparatus includes four developing devices for respective colors. Any one of four developing devices serves to carry out the printing operation of forming an image on a printing medium, and to supply a developer to an image carrier during the operation of forming an image for lubrication on the image carrier. The developing device used in the lubricating operation has a relatively higher consumption of developer than the other developing devices, and accordingly should be replaced more often than other developing devices. Therefore, a user has an inconvenience of frequently replacing the specific developing device, and further if a user does not have a deep knowledge about the operational principle of the image forming apparatus, a user may distrust the quality of the product.
Also, the color image forming apparatus is operated such that until an image for lubrication formed on the image carrier passes by all of the developing devices arranged in a downstream side of the image carrier, the next printing operation cannot be performed. Thus, a printing speed in the successive printing operation is deteriorated.
Further, while an image for lubrication formed on the image carrier passes by the developing devices arranged in a downstream side of the image carrier, the image for lubrication may be moved to the developing devices, and may contaminate the developing devices, which causes deterioration of image quality at the next printing operation.